Put a small amount of water in the pixie cup. Put the pixie cup in a baggy and close the baggy. Tape the baggy with the cup of water inside of it to a window that the sun comes in. What happens? With the heat of the sun, the water evaporates from the cup which you can not see and condenses on the inside of the bag into little water droplets. These droplets eventually drip down to the bottom of the bag.
This is what happens to the water in our creeks, streams, rivers, lakes and oceans. The water evaporates into the air and rise with the heat of the sun. It condenses into small droplets into what we see as clouds. When the droplets become to heavy, they fall to the ground as rain or snow.